Non-magnetic steels



United States Patent 3,383,203 NON-MAGNETIC STEELS Karl Giite Baggstriim, Karlskoga, Sweden, assignor to Aktiebolaget Bofors, Bofors, Sweden, a corporation of Sweden No Drawing. Continuation-impart of application Ser. No. 330,587, Dec. 16, 1963. This application Jan. 18, 1967, Ser. No. 610,009

Claims priority, application Sweden, Dec. 19, 1962, 13,711/62 6 Claims. (Cl. 75-128) ABSTRACT OF THE DISCLOSURE The present invention relates to a non-magnetic steel having desirable properties, particularly high impact strength, and to a method of producing said non-magnetic steel. Such steel is used for, among other things, the manufacture of retaining rings used in the electrical industry.

The steels consist essentially of carbon 0.50-0.80%, manganese 9.018.0%, silicon ODS-0.80%, chromium 20-60%, nickel 7.0-ll.0%, vanadium 0.60-1.0%, and the remainder iron.

The application is a continuation-in-part application based upon copending application Ser. No. 330,587 filed Dec. 16, 1963, now abandoned.

It is generally known that the non-magnetic, austenitic types of steel normally have a comparatively low tensile strength, and this, of course, limits the usefulness of such kinds of steel. When it has been desired to prepare a steel having both non-magnetic properties and a high tensile strength, austenitic types of steel were subjected to coldworking. However, such cold-Working requires much skill and experience, and there is still always some uncertainty in regard to the uniformity of the properties of the product. Moreover, if large units of steel are to be coldworked, special expensive machinery is required.

Studies in this field have therefore been directed toward eliminating cold-working, and through suitable heat treatment, consisting of solution treatment and precipitation hardening of certain alloys, considerable improvements have been obtained so as to obtain nonmagnetic steel of high tensile strength. However, all alloys hitherto known which have been subjected to this treatment have had poor impact strength.

In the following Table I, information is given about a number of alloys which, after solution treatment and precipitation hardening, have shown a high tensile strength, as measured by the yield point, but poor impact strength.

3,383,203 Patented May 14, 1968 tion R148. The impact strength was determined at +20 C. and the results are stated in kpm./cm.

It is accordingly an object of the present invention to provide a non-magnetic, austenitic steel having high tensile strength and high impact strength.

It is a further object of this invention to provide austenitic steels of specified composition which, when subjected to suitable treatment comprising solution and precipitation hardening will be changed into non-magnetic,

austenitic steels having both high tensile strength and high impact strength.

These and further objects of the invention will become apparent from the following description.

I have discovered that the objects of this invention can be achieved by subjecting alloys of the following composition:

Percent Carbon 0.50-0.80 Silicon 0.05-0.80 Manganese 9.0-l8.0 Chromium 2.0-6.0 Nickel 7.0-ll.0 Vanadium 0.60-l.0

and the remainder iron, together with the usual impurities in this type of steel, to solution treatment and precipitation hardening.

Preferably, the alloys have the following composition:

Percent Carbon 0.60-0.70 Silicon 0.05-0.50 Manganese 9.0-13.0 Chromium 4.0-5.0 Nickel 8.0l0.0 Vanadium 0.70-0.95

and the remainder iron, together with the usual impurities in this type of steel.

The austenitic steels of desired composition were solution treated and precipitation hardened by (l) annealing at a temperature of about 1150 C. for

about one hour,

(2) quenching in Water,

(3) annealing at a temperature of about 650 C. for

about 8 to 10 hours, and

(4) cooling in air.

The austenitic steels so treated were non-magnetic and had high tensile strengths and impact strengths greater than 5.5 kpm./crn.

Some examples of steel according to the present invention are shown in the following Table II.

The yield point, 0' has been defined as the load at which a non-proportional elongation corresponding to 0.2% of the original length of the test bar takes place. It is stated in kp./mm. and has been determined in an entirely conventional way, see ISO Recommendation R82. The impact strength tests were carried out with so-called V test bars in Charpy equipment, in accordance with a procedure which conforms entirely to ISO Recommenda- TABLE II Type Composition, percent Yield point Impact of do strength steel 0 Si Mn Cr Ni V lip/mm. Kcv+20 0.,

lrprn/cm.

H; 0.6 0.10 9.3 4.4 8.8 0.85 88.5 7.8 I 0.65 0.08 12.9 4.4 8.8 0.83 87.9 8.0 J 0.67 0.46 9.9 4.1 8.7 0.85 87.3 6.7 K 0. 69 0. 28 10. 4 4. 2 8. 7 0.86 92.2 5. 5

A comparison of the data in Tables I and II shows that non-magnetic, austenitic steels produced according to the invention, while having high tensile strength, also have greater impact strengths compared to the types of steels previously used in this connection.

Steels having compositions that do not meet the com position requirements of this invention (such as those disclosed in Belgian Patent 518,985 and US. Patent 2,865,740), when subjected to solution treatment and precipitation hardening, are not converted into steels having the high impact strengths as the non-magnetic austenitic steels of this invention.

What is claimed is:

1. A non-magnetic, austenitic steel having a high tensile strength and a high impact strength and having a composition consisting essentially of:

Percent Carbon 0.50-0.80

Silicon 0.05-0.80

Manganese 9.0-18.0 Chromium 2.0-6.0 Nickel 7.0-11.0 Vanadium 0.601.0

and the remainder iron.

2. A steel according to claim 1, wherein the composition consisting essentially of:

Percent Carbon 0.60-0.70 Silicon 0.05-0.50 Manganese 9.0-13.0 Chromium 4.0-5.0 Nickel 8.0-10.0 Vanadium 0.70-0.95

and the remainder iron.

. 4 3. A steel according to claim 2, which has an impact strength of at least 5.5 kpm./cm.

4. A steel according to claim 2, which has an impact strength of 8.0 kpm./cm. and consists essentially of:

Percent Carbon 0.65

Silicon 0.08

Manganese 12.9 Chromium 4.4

Nickel 8.8

Vanadium 0.83

Iron 72.3

5. A steel according to claim 1 which has been precipitation hardened.

6. A steel according to claim 2 which has been precipitation hardened.

References Cited UNITED STATES PATENTS HYLAND BIZOT, Primary Examiner. PAUL WEINSTEIN, Assistant Examiner. 

